Well, what about failures like me that can't even do 1 trial? And 15 years later still can't do it. Cure my spasticity and I'll tell you how many trials are needed. This is a case of extreme cherry picking of survivors that can do reach-to-grasp tasks.
How many trials are needed in kinematic analysis of reach-to-grasp?—A study of the drinking task in persons with stroke and non-disabled controls
Journal of NeuroEngineering and Rehabilitation volume 18, Article number: 101 (2021)
Abstract
Background
Kinematic analysis of the 3D reach-to-grasp drinking task is recommended in stroke rehabilitation research. The number of trials required to reach performance stability, as an important aspect of reliability, has not been investigated for this task. Thus, the aims of this study were to determine the number of trials needed for the drinking task to reach within-session performance stability and to investigate trends in performance over a set of trials in non-disabled people and in a sample of individuals with chronic stroke. In addition, the between-sessions test–retest reliability in persons with stroke was established.
Methods
The drinking task was performed at least 10 times, following a standardized protocol, in 44 non-disabled and 8 post-stroke individuals. A marker-based motion capture system registered arm and trunk movements during 5 pre-defined phases of the drinking task. Intra class correlation statistics were used to determine the number of trials needed to reach performance stability as well as to establish test–retest reliability. Systematic within-session trends over multiple trials were analyzed with a paired t-test.
Results
For most of the kinematic variables 2 to 3 trials were needed to reach good performance stability in both investigated groups. More trials were needed for movement times in reaching and returning phase, movement smoothness, time to peak velocity and inter-joint-coordination. A small but significant trend of improvement in movement time over multiple trials was demonstrated in the non-disabled group, but not in the stroke group. A mean of 3 trials was sufficient to reach good to excellent test–retest reliability for most of the kinematic variables in the stroke sample.
Conclusions
This is the first study that determines the number of trials needed for good performance stability (non-disabled and stroke) and test–retest reliability (stroke) for temporal, endpoint and angular metrics of the drinking task. For most kinematic variables, 3–5 trials are sufficient to reach good reliability. This knowledge can be used to guide future kinematic studies.
Background
Analysis of multi-joint 3D kinematics is needed to understand the underlying mechanisms of the altered movement strategies commonly seen post stroke [1]. Unlike traditional clinical assessments, objective measures of movement quality allow differentiation between behavioral recovery and compensation in evaluation of treatment effects [2,3,4]. Here, the kinematic analysis can provide detailed and objective information about movement performance and movement quality during everyday activities, such as reach-to-grasp [5, 6].
Reach-to-grasp is frequently used in daily activities and its performance in non-disabled individuals is characterized by efficient spatiotemporal coordination of the arm and hand segments for transport and grasping [7]. Regaining arm- and hand function post-stroke is one of the highest priority goals in rehabilitation, and still about 65% of the patients with hemiparesis have impaired ability to reach, grasp and handle objects at 6 months after stroke onset [8]. Motor performance of reach-to-grasp tasks in the stroke population shows longer movement time, lower peak velocity, decreased elbow extension, greater arm abduction and trunk displacement, and decreased smoothness as compared to non-disabled controls [5, 9,10,11]. Among the reach-to-grasp tasks, drinking from a glass has, due to its ecological validity and ease of standardization, been recommended as a functional task for quantifying quality of movement in stroke rehabilitation research [12].
Another aspect that needs to be considered in performance of daily purposeful tasks is variability of movements. Variability is inherent in human movement control, i.e. different neuromotor processes are available to produce automatic movement strategies needed for achieving goals in daily life [13]. The concept of movement variability is defined as typical variations in motor performance when a task is repeatedly being executed [14], which is something that needs to be taken into account when conducting clinical research studies. Optimal movement variability is crucial for healthy motor control [13, 15]. A high level of automaticity and relatively constant variability is, however, expected when a well-known activity is repetitively performed [16].
Requests for standardization of kinematic analysis of upper extremity movements have been highlighted [11] and for research purposes several efforts have been made to agree on which tasks to study and which systems and metrics to use [5, 9,10,11,12]. Clinimetric properties, including reliability, validity and responsiveness, have been reported for some kinematic metrics [9, 11, 17, 18] although more studies are needed [19, 20]. One aspect of reliability that has been sparsely investigated is the performance stability of selected variables within a session of a series of trials. Most of the studies of reach-to-grasp tasks in stroke populations include 3–10 trials per task although in few studies up to 20 trials have been reported [5, 11]. A recent consensus on kinematic studies in stroke recommended at least 15 trials to be collected, both for 2D performance assays and 3D functional tasks [12].
Hence, the question of how many trials that are needed to reach performance stability of kinematic measures in goal-directed reach-to-grasp tasks remains. A previous study analyzing movement performance during fast pointing in non-disabled participants, demonstrated that 3 trials were required to reach good within-trial reliability for movement time and peak velocity, whereas up to 47 trials were required for trajectory metrics [21]. Another study in persons with subacute stroke, where also 3D motion capture was used, reported that 5 trials was sufficient to get reliable results for reaching kinematics [22].
To our knowledge, no studies have defined the number of trials needed to achieve performance stability, i.e. good reliability, in kinematic measures of goal-directed reach-to-grasp tasks, nor has this been investigated in people with disabilities. Thus, the primary aim of this study was to determine the number of trials needed to reach good performance stability of the kinematic variables during the drinking task in non-disabled people and in a sample of individuals with chronic stroke. Further, the performance stability over the set of multiple trials was investigated. In addition, the between-sessions test–retest reliability of selected kinematics in a sub-sample of individuals with stroke was established.
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